This invention relates generally to voltage regulators, and more specifically to one for regulating the output voltage of an alternating current generator used on a motor vehicle for supplying the electrical loads thereon.
Vehicular generator output voltage regulating systems have been known and used extensively which include a semiconductor switch such as a transistor. Connected in series with the field winding of the generator, the switch is repeatedly turned on and off at controlled time intervals, causing the generator field winding to be energized so as to hold the generator output voltage practically constant. The following two different methods have been suggested and used for on-off control of the switch.
One such known method, according to Japanese Unexamined Patent Publication No. 54-30416, teaches to detect the output voltage of the generator. The switch is opened when the generator output voltage is higher than a desired level, and closed when otherwise. The switch is repeatedly turned on and off in response to sensed voltage changes so as to hold the generator output voltage at the desired value. This known method offers the advantage of simplicity in circuitry. Offsetting this advantage, however, is a serious drawback that arises in the event of a rapid drop in the generator output voltage due to an abrupt rise in energy requirement from a load or loads. Thereupon the generator is caused to demand such a high driving torque from the vehicle engine that it can noticeably slow down, hampering the smooth or safe driving of the vehicle.
Bowman et al. U.S. Pat. No. 4,636,706 represents the second known method which employs an up-down counter responsive to the relative magnitudes of the actual output voltage of the generator and the desired regulated output voltage of the generator. The counter is driven in an increasing direction when the actual generator voltage is below the desired regulated value, and in a decreasing direction when the actual generator voltage is above the desired regulated value. The instantaneous count of the counter determines the time during which the semiconductor switch is closed, and hence the pulse duration of the voltage applied to the generator field. The on time of the switch is shortened when the actual generator voltage is above the desired value, and extended when the actual generator voltage is below the desired value.
The Bowman et al. method overcomes the drawback of the first described method of generator voltage regulation. The bidirectional counter in use permits fine adjustment of the rate at which it is incremented and decremented, in order to correspondingly vary the rate at which the pulse durations of the voltage applied to the generator field are changed. No inconveniently abrupt change in the torque requirement of the generator is therefore to occur. This second known method has its own shortcoming, however. It requires highly complex, expensive circuitry for control of the bidirectional counter which must perform the dual purpose of extending and shortening the pulse durations of the voltage applied to the generator field winding.